Inertia operated bolt lock



D. M. WILLIAMS INERTIA OPERATED BOLT LOCK July 12, 1949.

3 Sheets-Sheet l Filed Nov. 6, 1947 July 12, 1949 n D. M. WILLIAMS 2,476,232

INEERTIA OPERATED BOLT LOCK Filed Nov. 6, 1947 3 Sheets-Sheet 2 July 12, 1949. D. M. WILLIAMS INERTIA OPERATED BOLT LOCK 3 Sheets-Sheet 3 Filed NOV. 6, 1947 "PMA W M im.,

Patented July 12, 1949 K @aldea/tin O'f'f on discharge Sai@ earmt "in 1 n cq 'prises' top 3 the top wall thereof. It will be understood, however, that the shoulder 2| may be formed by Welding or otherwise securing a separate member at the rear end of a relief-recess extending through out the length of the top wall of the receiver.

A breechblock indicated generally at 23, is adapted to be supported in the receiver for both longitudinal and pivotal movement and to this end the inside faces of the respective side walls |1 and I9 of the receiver I0 are provided with longitudinal grooves 24 and 25 respectively, each of which is substantially rectangular in cross section and adapted to slidingly Support a guidemember 26 and 21 respectively. The guide-member 26 comprises a bar substantially rectangular in cross section and arranged to engage in a longitudinal groove (not shown) of corresponding cross section formed in vthe forward end of the breechblock, whereas the guide-member 21 constitutes the body-portion of the finger-piece 28 which is used for manually retracting the breechblock, the guide-member 21 being adapted also to engage in a longitudinal groove (not shown) of corresponding cross section formed in the forward end of the breechblock. The rear end of each guide-member is provided with a transverse aperture 29 and 39 respectively, each being adapted to be arranged in axial alignment and to accommodate the respective opposite ends of a transverse pivot-pin 3|. connecting the rear ends of the guide-members to the breechblock and to this end is adapted to pass transversely through suitable rocker-shaped cam-slots 32 formed in the opposite depending spaced parallel sides 33 of the breechblock, the guide-members 26 and 21 being pivotally secured thereto on the outer faces of the respective sides 33 of the breechblock, as clearly shown in Fig. 5. When the breechblock is locked in breech-closing position as shown in Figs. 2 and 3, the transverse pivot-pin 3| of the guide-members 26 and 21 is adjacent the forward end of the rocker-shaped cam-slot 32 of the breechblock and is adapted to be moved rearwardly in the horizontal reach of the slot by manual actuation of the guide-members 26 and 21 without affecting the breechblock. However, when the pivot-pin subsequently moves into the upwardly-and-rearwardly-sloping portion of the cam-slot, the breechblock is pulled down out of locking engagement with the receiver. For brevity, the pivot-pin and cam-slot connection between the guide-members 26 and 21 and the breechblock is hereinafter referred to as a lost-motion linkage.

The breechblock 23 of the present embodiment is provided with the usual type of axially-aligned reciprocating firing-pin 34 and a reciprocating ejector 35, the rear end of which is seen in Figs. 2 and 3. The top of the breechblock comprises a cylindrical surface of revolution, the curvature of which conforms substantially to that of the relief-recess 22 in the underside of the top wall o'f the receiver and is provided at its rear end with an integral upwardly-projecting lockinglug 36 adapted to be moved into and out of engagement with the chamber-extension of the chamber-unit, in the manner and for the purpose hereinafter described.

' The breechblock-actuating means comprises an inertia-bar, action-spring and link assembly supported, in the main, in the buttstock of the firearm. The link of this assembly is indicated at 31, its forward end being adapted to extend between the inside faces of the depending sides 33 of the breechblock and to be pivotally connected The latter is provided for 4 to the latter by the transverse pin 3|. The rear end of the link 31 is pivotally connected to the forward end of an intertia-bar 38 which is slidingly supported in a sleeve 39 threaded or otherwise seuured at its forward end to the rear wall of the receiver and projecting rearwardly through an axial aperture 40 in the buttstock. The rear end of the sleeve 39 projects into the forward end of a longitudinal counterbore 4| of the aperture 40,- the counterbore 4| being adapted to accommodate a second sleeve 42 which is threadedly secured at its forward end to the rear end of the sleeve 39 and which is closed at its rear end by a screw-cap or plug 43. The sleeve 42 is adapted to support the action-spring 44, the rear end of which engages against the plug 43. The forward end of the action-spring engages an annular flange 45 formed at the forward end of an inertiaweight 46 which, in turn, extends rearwardly from and is suitably secured to the rear end of the inertia-bar 38.

One embodiment of the improved chamber-unit of this invention is indicated generaly at 41, and as shown in Figs. 2, 3, 4 and 1, comprises a chamber-member 43 and chamber-extension 5|, hereinafter described. The former consists of a substantially-cylindrical sleeve having a reduced neck-portion 49 at its forward end and an annular shoulder 50 at its rear end, the shoulder 50 being provided with exterior screw threads whereby the rear end of the chamber is adapted to be threadedly secured to the forward end of the chamber-extension 5|. Referring again to the chamber-member '48, the over-all length of the latter is considerably in excess of the length of a cartridge. Further, the inside diameter of the chamber-member is such that a cartridge is adapted to make a snug fit therein, whereas the outside diameter of the chamber-member is such that the latter will make a substantially-gas-tight sliding fit in a longitudinal counterbore 52 formed axially in the breech-end of the barrel 2, the counterbore 52 having a portion 53 of reduced diameter at its forward end which intersects the rear end of the barrel-bore 54 and in which the neck-portion 49 of the chamber-member 48 is adapted to fit. As indicated in Fig. 2, when the chamber-unit 41 is in its normal forward position in the receiver-and-barrel assembly, the forward end of the neck-portion 49 of the chamber-member abuts the substantially-annular squareshoulder 55 formed at the intersection of the reduced portion 53 of the counterbore 52 and the rear end of the barrel-bore 54, the annular shoulder 50 at the rear end of the chamber-member being in abutting engagement with the breechend |20 of the barrel.

The chamber-extension 5| of the chamberunit may be secured rigidly to the rear end of the chamber-member 48, and to this end the forward end of the chamber-extension comprises an annulus 56 having internal threads adapted to be engaged with the externally-threaded shoulder 50 of the chamber-member, whereby the forward ends or faces of the annulus 56 and of the annular shoulder 50 of the chamber-members respectively lie in substantially the same vertical plane. Thus, when the chamber-unit is in its normal forward position in the firearm, the forward ends or faces of both the annular shoulder 50 and the annulus 56 will be in abutting engagement with the rear end |20 of the barrel, as shown in Fig. 2. Although a rigid connection between these two respective members of the chamber-unit is satisfactory, it will be underthe over-al1 lengthpffthe chamber-extension .5I

is such that Awhen .thechamlber-.unit-ll'l isin its normal #forward position -in the receiver-,and- Ybarrel assemb1y,;the rear lendgof .the chamberextension 5l is spaced forwardly of ythe xed transverseshoulder 2|of1the receiver -\a .predei -termined distance which is :but fa small :fraction :of the distance-moved by the ,breechblock during -its opening stroke, that ,isito say, from its forward,breech-closing:position to its rearmostposition-inthe receiver,;this small fractional distance being in the ratio 0f substantially 1 to 0.025 of the opening stroke of thebreechblock and corresponding to substantially 0.07;5. inch jfor an opening stroke of substantially 3 inches.

indicated in Fig. 7, the chamber-,extension `5| comprises a substantially-cylindrical sleeve' ,of uniform internal land rexternal diameters, the lforward end of which constitutes theaforesaid .annulus 56. The Outside Adiameter of the `Vchamber-extension corresponds substantially ft'o :y A

fthe diameterrofthe relief-recess 22 formed on the inside of the top wallof the receiver,.whereas Itlieinsidediameterof the chamber-extension is vsomewhat greater 'than the inside diameter y.of

.its vchamber-member, so that a red cartridge z,

.case will have azfree fitrthereinpthe inside diam- `eter of the extension corresponding substantially pto that ofthe. curved upper surface of the breechblock, as a consequence of which the chamberextension is adapted tovbeslidingly -guidedrand `of the sleeve; and a substantially-rectangular enlargement 59 intersecting'the rearfendof `the Islot and displaced transversely'to one side-thereof. The inverted-L-shaped locking-aperture '-51 is thus adapted to receive the locking-lug 36-of :corresponding shape vformedon the top of the 1 t'breechblock so as to lock the glatter in engagement with the chamber-extension. To this end, -.the rear end of theiinverted-L-shaped lockingaperture'5'l is'provided with an undercut beveled shoulder '6G-adapted` to be engaged by the beveled l shoulder El at theirearof the breechlblock locking-'lug 36 when fthe latter is elevated into the Adnverted-L-shaped `locking-aperture 51 -of the chamber-extension, as hereinafter described.

lReferring to Figs. 5, 6 and 7, the bottom of the sleeve-like chamber-extension 5I is slabbed off .or otherwise operated upon in such manner'that ithe left-hand side wall ofthe sleeve `is -formed `.with a substantially-straight longitudinal bottom .zedgen62 extending uninterruptedly from the rear :face of the annulus 56 tothe rearfend ofthe chamber-extension, the right-hand side wall -thereof being formed vwith-,alstraight bottom edge 63 which extends `V:from `the rear end of 'the .chamber-.extension ,forwardly a relatively-short .distance its forward end intersecting the ysubstantially-vertical rear .edge 64 of a clearance .cut-out 65 formed inztheright-handwall of the sleeve. Both the-bottom edge 62 .and the relatively-short .bottom edge 263 'of the .chamberi6 .extension lie-in ythe sameihorizontalsplane. l More- 'pven :the inside faces fof the respective; side walls .of the chamber-.extension are :milled or 4 other- -wise formed with substantially-rplanar vertical .sliir'faces 1616 and 151 irespectively which intersect :the corresponding :bottom :edges 62 and `63 of athe-side Wallsr an'diarefadapted tol lie in juxtaposiftion to the corresponding side wallsv of the :breechfblock, see Figs. 5 fand z 6, the planar-'vertical sur- .facec 'being adapted .to guiderthe vlatter' during t "its longitudinal :movement with .frespect to the chamber+,eXtensi0n, as fhereinafter described. .The planarverticalssurface:61 of the right-hand .wall :is zrecesse'd laterally toi form a longitudinal .guide,,groove?68. substantially rectangular in cross .section :and opening :inwardly to accommodate the v:extractor agli-9 lof '-the yibreechblock. In this :capacity Vthe .extractor constitutes, in eiect, a :spline niovablelongitudinally in the guide-groove *.68 and incorporating fthe Siunction of a key to prevent rotation rof :the chamber-unit with re- 'fspect -Vtlo the lbreechblock when the latter is ap- :proaching orreturningifrom theend of its rearward `v`excursion `in ithe receiver. When the .breech'block is:initsforwarwbreech-closing posiation, :the :extractor TSB yis adapted -to engage in a =learanc-egroove `560 of :similarcross section 4in .the annulus i515 of 'the `chamber-extension 5l .The .-'aforernentioned :aperture lor lcut-out 1'6'5 formedin theright-:hand-side wallfoflthe chamiber-:extension:member-is.dened at its rear end why fthe substanitallyevertical edge 6'4 and at its :forward :edge byltl're rear '.face of `the annulus 56. 'The upper edge 'i110 `of :the aperture A 65 `extends auninterruptedly ibetween the zrespective edge 64 and the rear face of the annulus and lies ina shorizontal plane .which :is :above `the horizontal :fplane of the longitudinal axis of the chamberextension, such `that when the kchamber-unit is ,l0 .assemblediin lthemeceiver:ofthe firearm, the'upper vedge "lll ofithelaperture 65-wil1 coincide substantially with the upper edge ofthe ejectionport l'lginthe right-hand sidewall of the receiver,

as indicated in Fig. 1.

The chamber-:extension l5l is adapted to be ,provided withresilient-means tohold the chamrber-t-,unit .in y:its normal forward position in the :receiver and tolreturn'thechamber-unit from its :rearmost 'position vin the .receiver to its normal .forward .position [and to `this end an aperture i'ldsfformed1in1theirearfiend of the chamber-ex- .tensioncextending longitudinally in the top wall :thereof the aperture `v:'l2zbeing adapted to be subestantiallyfoppositefthe transverse shoulder 2l of '.the receiver .when 'thechamber-unit is supported :therein,..as.vshown in lFigs. 2 and 3, Mounted in vtheaperture 1 2iis 'acoil-spring T3, the over-all length lof which :greater than the depth of the.aperture'lZf-so.that'a-portion ofthe rear end vof thespring:extendsrrearwardly beyond the rear -end :of zthe kchamber-extension. Consequently, awhenzfthe chamber-.unitris in its normal forward positionfin .therbarrel-treceiver assembly, the rear end ofthe spring 'is immediately opposite and ,preferably .in engagement with the transverse shoulder 2| lofithereceiver-so as to constantly .urge the chamber-unitfforwardly in the receiver. *Although 'butaone .return-spring T13 is shown in the .present yembodiment, it will be appreciated .that vone or morethan one may be used with equal success.

,Amodificationsof'the chamber-unit is indicated vgenerally at 15"inlFigs. 8 Ithroughll, and is characterized by `an articulated @connection between .the chambe11-'1nerriber and chamber-extension `of the aforesaid unit. Whereas the chamber-member 48 of the chamber-unit 41 is provided with an externally-threaded shoulder 50, the rear end of the chamber-member 16 of the chamber-unit is provided with a relatively-thick annular flange 11 which circumscribes a portion of the bottom side of the chamber-member. The flange subtends an angle which is of the order of 130, the right-hand end of the flange terminating in a substantially-square shoulder 18 which is disposed in a horizontal plane slightly below the horizontal plane through the longitudinal axis of the chamber-member; the opposite or lefthand end of the flange terminating in a substantially-square shoulder 19 which lies in a horizontal plane below the plane of the shoulder 18. Circumscribing the breech-end of the chambermember from the ilange-shoulder 19 to a point on the opposite side thereof are a pair of spaced parallel substantially-annular ribs 80 and 8| which are preferably formed integrally with the chamber-member, each rib being substantially rectangular in cross section. The right-hand end of the rearmost rib 30 terminates in a horizontal plane slightly above the horizontal plane of the longitudinal axis of the chamber-member, and is spaced vertically from the shoulder 18 a distance corresponding substantially to the vertical dimension of the extractor 69 of the breechblock to form a slot 82 to receive the forward end of the extractor when the breechblock is in its closed position. The corresponding end of the annular rib 8| is blended into the ilange 11 while the opposite or left-hand ends of the ribs 80 and 8i are blended into the corresponding end of the flange 11.

Referring to Fig. 8, the vertical plane of the front face of `the foremost annular rib 8| and of the front face of the flange 11 will be seen to be substantially co-extensive, as a consequence of which both of these respective faces are adapted to abut the rear end of the barrel when the chamber-unit 15 is in its normal forward position in the rearm.

The annular` ribs 80 and 8| are adapted to circumscribe an angle of substantially 220 and, in conjunction with the flange 11, are adapted to make articulated engagement with the forward end of the chamber-extension 83. The latter is substantially similar in all respects to the chamber-extension 5I of the chamber-unit 41 except as to the construction of its forward end. The latter comprises a substantially-semicircular arc 84, the left-hand end 85 of which terminates in the horizontal plane of the lower edge 86 of the chamber-extension, whereas the right-hand end 81 of the arc 84 terminates substantially in a horizontal plane of the longitudinal axis of the chamber-extension. The inner wall of the arcuate end 84 of the extension is provided with an annular groove 88 which is substantially rectangular in cross section and is adapted to receive the annular rib 80 on the rear end of the chamber-member to couple the two members in operative relationship. Since both the annular ribs 80 and 8| and the arcuate end of the chamberextension circumscribe angles of more than 180, the two members are assembled by engaging the right-hand end 81 of the extension in the extractor-slot 82 of the chamber-member and then swinging the arcuate end 84 of the extension downwardly into coupling engagement with the annular rib 80 of the chamber until the left-hand end 85 of the arcuate edge 84 engages the shoulder 19 ofthe chamber. The chamber-extension is thus locked to the chamber-member, although not rigidly, there being articulation of the order of two or three thousandths inches in the joint to compensate for any mis-alignment of the barrelbore and the chamber of the receiver.

The rear end of the chamber-extension is provided with a recessed groove 89 adapted to accommodate the extractor 69 of the breech- .block and to function as a keyway for the latter, whereby the chamber-extension is precluded from rotating clockwise relative thereto, as seen in Fig. 9, which circumstance, if permitted, would partially close the extractor-slot 82 and cause a jam. Moreover, rotation of the chamber-extension in a counterclockwise direction is positively prevented by engagement of the lefthand end 85 of the extension with the shoulder 19 of the chamber-member, as described above. The latter is, in turn, positively held from rotating in the breech-end of the barrel by means of a longitudinal key (see Figs. 8 and 9) which is supported in a longitudinal slot 9| formed in the bottom of the barrel-receiving aperture |80 in the front wall of the receiver, the key 90 being adapted to engage in a longitudinal keyway 92 provided in the bottom of the flange 11 of the chamber-member.

Although the chamber-unit 15 is characterized by an articulated joint between the chambermembers 16 and the chamber-extension 83, so as to compensate for variations in alignment of the barrel-bore and the chamber of the receiver, it will be understood that insofar as its function is concerned, the modied chamber-unit 15 operates substantially identically to the chamberunit 41.

The operation of the improved rearm of the invention may be described briey as follows. Assuming the elements of the firearm are in the positions shown in Fig. 2, with the chamberunit 41 in its normal forward position in the receiver-barrel assembly such that the forward end 49 of the chamber-member 48 is in abutting engagement with the shoulder 55 of the barrel-bore 54 and the rear end of the chamberextension 5| is forwardly of the shoulder of the receiver a distance corresponding substantially to 0.075 inch, the breechblock 23 is in its normal forward breech-closing position wherein the locking-lug 36 of the breechblock is engaged in the reversed-L-shaped locking-aperture 51 of the chamber-extension, the beveled shoulder 6| of the locking-lug being in engagement with the beveled shoulder thereof. Moreover, the lockinglug is securely held in the aperture 51 in the top wall of the chamber-extension by the breechblock-actuating means and more specifically by engagement of the transverse pivot-pin 3| of the action-link 31 in the cam-slots 32 of the breechblock, the pin being urged forwardly into engagement with the forward ends of the camslots by the force of the action-return spring 44. The phrase breechblock-actuating means as used herein shall be understood to include the inertia-bar, action-spring and link assembly as well as its transverse pivot-pin and cam-slot connection to the breechblock, which is hereinafter referred to as the lost-motion connection, between the link of the assembly and the breechblock. When the firearm is discharged, the gases created by the discharged cartridge build up within the bore of the barrel and within the forward end of the chamber-member 48 of the chamber-unit, and quickly reach a sufiicientlyhigh pressure to overcome the combined resistso? as to drive the chamber-unit' l4l; including the locked" breechblock and the breechblockactuating assembly, rearwardly in the receiver untill the rear end" of? the chamber-extension I strikes sharplyv against the transverse shoulder 2l of thel receiver; thereby compressing the chamber-'unitv return-spring T3- mounted in the rear end of'the charnlrner=extensionl During this initial rearward movement of the chamber-uni@ breechblock andbreechblock-actuating assembly,

engagement of tlie transverse pivot-'pin of the spring-loaded* action-link in the cam-slots of' the breechblock holds the breech-block firmly inv locked engagement with'theI chamber-extension.. Moreover', the-predetermined'and extremely short' distance which the chamber-unit moves rearwardly'v is such that bythe time the latter has' been stopped' Ibythe' fired shoulder 2| ofthe receiver` andthe^breech-bolt has been unlocked by the action-ofthe lost-motion linkage, the 4pressure inthebore-andfcounterbore of the'barrelf' Engagement" has dropped substantially to Zero'. ofi the chamber-unit with' the shoulder 2l positively stops-y fur-then rearward-I movement ofu the chamber-'unit asfwel' as that of the breechblock which is.v lecked thereto.- The breechblockactuating means-is, however, freef to continue-its rearward. movement and onA so' doing', draws the transverse pin 311 of; thelost-motion connectionrearwardly in t'l'i'e'A cam-slots 32'- of* the ,breechblock; Theimmediate effect of' this action is to pull the'- locking-lug ofh the breechblockV out of* Itwillbe appreciated that as soon as' the fired? cartridge has-been withdrawn from the chambermember in. whiclithe cartridge makes a relatively-snug t into the chamber-extension in which' the firedoartridge-cafse has a-free fit, the chamber-uniti is= freed-l and' thereupon will be moved forwardly into its normal forwardfposition: by-the force of 'itsf compressed return-spring 13; the inertia developed by the: forward movement' of the chamber-unitacting simultaneously with" andi in'` aA direction counter tothe` inertia force ofi the rearwardly-moving loreechblock` and' action-rod assembly. 'Iliev reeoilforce ofthe rearm is in part; therefore, the resultant ofv these. two` oppositely-act-ing inertia forces and lessA than the` inertia` of the breechblock and'v action-rod assembly: As the breechblock` continuesv its: rearward movement in the receiver, the` action-spring Mof thebl'eechblock-actuating assembly is compressedA andthe extracted cartridge-oase is c'arriedrearwardly into the-chamber-extension 51| to a position substantially oppositeI the clearance aperture thereof which, as l pointed out above; is v substantially co-extensive with the ejection-port lil in the right-hand'wall of the receiver'. At' the end of" its rearward eX- cursion in the receiver; the breechblock is brought toa stopfimmediately adjacent the rear wall: thereof; Simultaneously, the rear end of the spring-mounted ejector-pin 35' is brought sharply into` engagement with the rear wall of` the receiver so astol bey thrust forwardly force- 1,0, fully against the rim of the. extracted cartridge-r case,. whereupon the latten is. pivotally ejected` out"ofthejectionr-portjl.of, the receiver. The forcev of the compressed action-spring lllU thereupon., overcomes. any. residual inertia` of thef breeclrbloc-k.A andi moves the l latter forwardlyv in-y theireceiver.

At this, point it, should beA pointed out. thatv the rearm..dees not emplOy theusual relatively.- heavy recoilvspring but that, the relatively-light.v action-spring? 44 serves both as aspring, toretard@` the rearward, mdr/ement., of.A the breecbblock` andY tdmove the latten, forwardly. in thereceiver, this dual functionof, the, action-spring., being made-ppossible` bythe factfthat the-breechblock and the breechblock.-actuatingassembly` are the only:y elements which. move,n rearwardlyi in? the receiverI throughout the entire length of thefl opening; stroke; the chamber-units 41, having but' an.. ex tremely. small.: rearward4 movement and.- being; adapted to set` up, a-.c01lnten-reeoil forceduring; part. of the, rearward",- excursion: of, the breech,- block. Thus; the initial reeoill which, is.- characterized by a blow against the shoulder-l off the -shooter when the firearm islred, is relatively small. Moreover, the secondary recoil which; characterizes iirearms` embodying a: conventional; barrel and ,barrel-extension., assemblyis t substan-A tially eliminated.

The expansion forceof the-compressed actionspring ld` acting, on -thainertia-bar 3.8- andL action-:- link assembly, moves: the` breechblockV forwardlyin the receiver, the transverse pin ofthe actionlink riding, ini thecam-slots. 32 ot the` breechblock. Simultaneously, afresh cartridge-isl autofed from thef tubular magazine |`3 and introduced into the chamber-member 411 between the spaced parallel edges 62 and 63 ofits` open bottom by:v the, forwardly-moving breechblock. and suitable cartridge-carrier elevating-means (not shown),y inz a manner conventional witlry automatic nrearms of this generaltype;

From; the' foregoing: description and drawings, it will-be clear that thefprovision off the improved chamber-unit of thisy invention having any extremely-shont rearward. movement, has eliminated the need: for, a1 long; rearwardly-extending substantially-horizontal chamber in the receiver, as. a consequence ofy which:A the: receiver may be formed with adownwardly-and-rearwardlycurved upper surfaceto give they firearm a pleasing streamlined appearance.- Moreover, the` chamber-unit permits. the; use. of: a: fixed barrel'- in, an automatic 1'earm'5-wh-ich'- construction insures better sighting, since the receiver and' barrel. constitute a, rigid; unit. barrel of the improved'rearm of this invention is fixed to theV receive-r1` and-2` the,l rearward excursion of the breechblock is discontinuous, i. e.,

The firing-elements' of the' firearm are; again inposition preparatory." to firing a fresh cartridgathelatter-having beeny Further, since the' 1 l moves rearwardly initially an extremely small fraction of its total opening stroke whereupon 1t is stopped and subsequently restarted, the shock of recoil of the firearm when fired is reduced to a minimum. And as an additional feature, since the movement of the chamber-unit is but a small fraction of the bolt travel, the chamber-unit never acquires sufficiently high velocity to damage the stop-shoulder of the receiver, while the rearward movement of the breechblock, subsequent to cessation of its rearward excursion at the stop-shoulder of the receiver, is dampened by the resistance offered by the action-return spring and hence brings up at the rear end of the receiver with minimum residual inertia.

The invention may be carried out in other specific ways than those herein set forth without departing from the spirit and essential characteristics of the invention, and the present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming Within the meaning and equivalency range of the appended claims are intended to be embraced therein.

I claim:

1. In an automatic firearm, the combination including a receiver; a barrel fixed to said receiver; a breechblock reciprocably mounted in said receiver; a chamber-unit comprising a chamber-member slidably supported in said barrel and a chamber-extension projecting rearwardly into said receiver; means to positively stop the rearward movement of said chamber-unit on discharge of said firearm after said chamber-unit has moved rearwardly a distance equal to a small fraction of the opening stroke of said breechblock; and breechblock-actuating means connected to said breechblock, said breechblockactuating means being arranged to move rearwardly with said breechblock and simultaneously to hold said breechblock in locked engagement with the said chamber-extension of said chamber-unit when said firearm is discharged, whereby said breechblock and said chamber-unit move rearwardly concurrently through the said fractional distance of the opening stroke of said breechblock, said rearwardly-moving breechblock-actuating means being arranged thereafter to unlock said breechblock from the said chamber-extension immediately succeeding cessation of movement of said breechblock and said chamber-unit by engagement thereof with said positive stop and to draw the immobile breechblock rearwardly in said receiver through the remaining portion of its opening stroke.

2. In an automatic firearm, the combination including a receiver; a barrel xed to said receiver; a breechblock reciprocably mounted in said receiver; a chamber-unit comprising a chamber-member slidably supported in said barrel and a chamber-extension projecting rearwardly into said receiver; means to positively stop the rearward movement of said chamber-unit on discharge of said rearm after said chamber-unit has moved rearwardly a distance equal to a small fraction of the opening stroke of said breechblock; breechblock-actuating means connected to said breechblock, said breechblock-actuating means being arranged to move rearwardly with said breechblock and simultaneously to hold said breechblock in locked engagement with the said chamber-extension of said chamber-unit when said firearm is discharged, whereby said breechblock and said chamber-unit move rearwardly concurrently through the said fractional distance of the opening stroke of said breechblock, said rearwardly-moving breechblock-actuating means being arranged thereafter to unlock said breechblock from the said chamber-extension immediately succeeding cessation of movement of said breechblock and said chamber-unit by engagement thereof with said positive stop and to draw the immobile breechblock rearwardly in said receiver through the remaining portion of its opening stroke; and resilient-means carried by said chamber-unit and arranged to abut said stopmeans to return said chamber-unit to its normal position in said barrel immediately following disengagement of the breechblock from said chamber-extension.

3. In an automatic rearm, the combination including a receiver; a barrel xed to said receiver; a breechblock reciprocably mounted in said receiver; a chamber-unit comprising a chamber-member slidably supported in said barrel and a chamber-extension projecting rearwardly into said receiver; means to positively stop the rearward movement of said chamber-unit on discharge of said firearm after said chamber-unit has moved rearwardly a distance equal to a small fraction of the opening stroke of said breechblock; breechblock-actuating means connected to said breechblock, said breechblock-actuating means being arranged to move rearwardly with said breechblock and simultaneously to hold said breechblock in locked engagement with the said chamber-extension of said chamber-unit when said firearm is discharged, whereby said breechblock and said chamber-unit move rearwardly concurrently through the said fractional distance of the opening stroke of said breechblock, said rearwardly-moving breechblock-actuating means being arranged thereafter to unlock said breechblock from the said chamber-extension immediately succeedingI cessation of movement of said breechblock and said chamber-unit by engagement thereof with said positive stop and to draw the immobile breechblock rearwardly in said receiver through the remaining portion of V its opening stroke; and an action-spring associated with said breechblock-actuating means arranged to resist the rearward movement of said chamber-unit and-said breechblock and to return said breechblock to its normal forward position in said receiver.

4. In an automatic firearm, the combination including a receiver; a barrel fixed to said receiver; a breechblock reciprocably mounted in said receiver; a chamber-unit comprising a chamber-member slidably supported in said barrel and a chamber-extension projecting rearwardly into said receiver; means to positively stop the rearward movement of said chamberunit on discharge of said rearm after said chamber-unit has moved rearwardly a distance equal to a small fraction of the opening stroke of said breechblock; breechblock-actuating means connected to said breechblock, said breechblockactuating means being arranged to move rearwardly with said breechblock and simultaneously to hold said breechblock in locked engagement with the said chamber-extension of said chamber-unit when said firearm is discharged, Whereby said breechblock and said chamber-unit move rearwardly concurrently through the said fracsaid receiver; a chamber-unit comprising a chamber-member slidably supported in said barrel and a chamber-extension projecting rearwardly into said receiver; a stop-shoulder in said receiver, said shoulder being located rearwardly of the breech-end of said barrel a distance comprising a small fraction of the opening stroke of said breechblock, said shoulder being arranged to project into the path of the rearwardly-moving chamber-extension to stop the rearward movement thereof on discharge of said firearm; and breechblock-actuating means connected to said breechblock, said breechblock-actuating means being arranged to move rearwardly with said breechblock and simultaneously to hold said breechblock in locked engagement with the said chamber-extension of said chamber-unit when said rearm is discharged, whereby said breechblock and said chamber-unit move rearwardly concurrently through the said fractional distance of the opening stroke of said breechblock until said chamber-extension engages said stop-shoulder, said rearwardly-moving breechblock-actuating means being arranged thereafter to unlock said breechblock from the said chamber-extension immediately succeeding cessation of movement of said breechblock and said chamber-unit and to draw the immobile breechblock rearwardly in said receiver through the remaining portion of its opening stroke.

l0. In an automatic firearm, the combination including a receiver; a barrel fixed to said receiver, a breechblock reciprocably mounted in said receiver; a chamber-unit comprising a chamber-member slidably supported in said barrel and a chamber-extension projecting rearwardly into said receiver; a stop-shoulder in said receiver, said shoulder being located rearwardly of the broch-end of said barrel a distance comprising a small fraction of the opening stroke of said breechblock, said shoulder being arranged to project into the path of the rearwardly-moving chamber-extension to stop the rearward movement thereof on discharge of said firearm; breechblock-actuating means connected to said breechblock, said breechblock-actuating means being arranged to move rearwardly with said breechblock and simultaneously to hold said breechblock in locked engagement with the Said chamber-extension of said chamber-unit when said firearm is discharged, whereby said breechblock and said chamber-unit move rearwardly concurrently through the said fractional distance of the opening stroke of said breechblock until said chamber-extension engages said stopshouider, said rearwardly-moving breechblockactuating means being arranged thereafter to unlock said breechblock from the said chamberextension immediately succeeding cessation of movement of said breechblock and said chamberunit and to draw the immobile breechblock rearwardly in said receiver through the remaining portion of its opening stroke; and resilient-means carried by said chamber-extension and arranged to abut said stop-shoulder to return said chamber-unit to its normal position in said barrel immediately following disengagement of the breechblock from said chamber-extension.

1l. In an automatic firearm, the combination including a receiver; a barrel fixed to said receiver; a breechblock reciprocably mounted in said receiver; a chamber-unit comprising a chamber-member slidably supported in said barrel and a chamber-extension projecting rearwardly into said receiver; a stop-shoulder in said 16 receiver, said shoulder being located rearwardly of the breech-end of said barrel a distance comprising a small fraction of the opening stroke of said breechblock, said shoulder being arranged to project into the path of the rearwardly-moving chamber-extension to stop the rearward movement thereof on discharge of said firearm; breechblock-actuating means connected to said breechblock, said breechblock-actuating means being arranged to move rearwardly with said breechblock and simultaneously to hold said breechblock in locked engagement with the said chamber-extension of said chamber-unit when said firearm is discharged, whereby said breechblock and said chamber-unit move rearwardly concurrently through the said fractional distance of the opening stroke of said breechblock until said chamber-extension engages said stopshoulder, said rearwardly-moving breechblockactuating means being arranged thereafter to unlock said breechblock from the said chamberextension immediately succeeding cessation of movement of said breechblock and said chamberunit and to draw the immobile breechblock rearwardly in said receiver through the remaining portion of its opening stroke; resilient-means carried by said chamber-extension and arranged to abut said stop-shoulder to return said chamber-unit to its normal position in said barrel immediately following disengagement of the breechblock from said chamber-extension; and an action-spring associated with said breechblock-actuating means arranged to resist the rearward movement of said chamber-unit and said breechblock and to return said breechblock to its normal forward position in said receiver.

l2. In an automatic firearm, the combination including a receiver; a barrel fixed to said receiver; a breechblock reciprocably mounted in said receiver; a chamber-unit comprising a chamber-member slidably supported in Said barrel and a chamber-extension projecting rearwardly into said receiver; a stop-shoulder in said receiver, said shoulder being located rearwardly of the breech-end of said barrel a distance comprising substantially 0.025 of the opening stroke of said breechblock, said shoulder being arranged to project into the path of the rearwardly-moving chamber-extension to stop the rearward movement thereof on discharge of said firearm; and breechblock-actuating means connected to said breechblock, said breechblockactuating means being arranged to move rearwardly with said breechblock and simultaneously vto hold said breechblock in locked engagement with the said chamber-extension of said chamber-unit when said rearm is discharged, whereby said breechblock and said chamber-unit move rearwardly concurrently through the said fractional distance of the opening stroke of said breechblock until said chamber-extension engages said stop-shoulder, said rearwardly-moving breechblock-actuating means being arranged thereafter to unlock said breechblock from the said chamber-extension immediately succeeding cessation of movement of said breechblock and said chamber-unit and to draw the immobile breechblock rearwardly in said receiver through the remaining portion of its opening stroke.

13. In an automatic firearm, the combination including a receiver; a barrel fixed to said receiver; a breechblock reciprocably-mounted in said receiver; a chamber-unit comprising a chamber-member slidably supported in said barrel and a chamber-extension projecting rearwardly into said receiver; a stop-shoulder in said receiver, said shoulder being located rearwardly of the breech-end of said barrel a distance comprising a small fraction of the opening 'stroke of said breechblock, said shoulder being arranged to project into the path of the rearwardly-moving chamber-extension to stop the rearward movement thereof on discharge of said firearm; and breechblock-actuating means comprising lostmotion linkage connected to said breechblock, said breechblock-actuating means being arranged to move rearwardly with said breechblock and simultaneously to hold said breechblock in locked engagement with the said chamber-extension of said chamber-unit when said rearm is discharged, whereby said breechblock and said chamber-unit move rearwardly concurrently through the said fractional distance of the opening stroke of said breechblock until said chamber-extension engages said stop-shoulder, the said lost-motion linkage of said rearwardlymoving breechblock-actuating means being arranged thereafter to unlock said breechblock from the said chamber-extension immediately succeeding cessation of movement of said breechblock and said chamber-unit and to draw the immobile breechblock rearwardly in said receiver through the remaining portion of its opening stroke.

14. In an automatic firearm, the combination including a receiver; a barrel xed to said receiver; a breechblock reciprocably mounted in said receiver; a chamber-unit comprising a chamber-member slidably supported in said barrel and a, chamber-extension projecting rearwardly into said receiver; a stop-shoulder in said receiver, said shoulder being located rearwardly of the breech-end of said barrel a distance comprising a small fraction of the opening stroke of said breechblock, said shoulder being arranged to project into the path of the rearwardly-moving chamber-extension to stop the rearward movement thereof on discharge of said rearm; and breechblock-actuating means comprising an inertia-bar and lost-motion linkage connected to said breechblock, said breechblock actuating means being arranged to move rearwardly with said breechblock and simultaneously to hold said breechblock in locked engagement with the said chamber-extension of said chamber-unit when said rearm is discharged, whereby said breechblock and said chamber-unit move rearwardly concurrently through the said fractional distance of the opening stroke of said breechblock until said chamber-extension engages said stop-shoulder, the said inertia-bar being arranged to continue the uninterrupted rearward movement of said lost-motion linkage, whereby the latter unlocks said breechblock from the said chamber-extension immediately succeeding cessation of movement of said breechblock and said chamber-unit and draws the immobile breechblock rearwardly in said receiver through the remaining portion of its opening stroke,

15. In an automatic firearm, the combination including a receiver; a barrel fixed to said receiver; a breechblock reciprocably mounted in said receiver; a chamber-unit comprising a chamber-member slidably supported in said barrel and a chamber-extension projecting rearwardly into said receiver; a stop-shoulder in said receiver, said shoulder being located rearwardly of the breech-end of said barrel a distance comprising substantially v0.025 of the opening stroke of said breechblocksaidshoulder being arranged to project into the path of the rearwardly-moving chamber-extension to stop the rearward movement thereof on discharge of said iirearm; and breechblock-actuating means comprising an inertia-bar and lost-motion linkage connected to said breechblock, said breechblock-actuating means being arranged to move rearwardly with said breechblock and simultaneously to hold said breechblock in locked engagement with the said chamber-extension of said chamber-unit when said firearm is discharged, whereby said breechblock and said chamber-unit move rearwardly concurrently through the said fractional distance of the opening stroke of said breechblock until said chamber-extension engages said stop-shoulder, the said inertia-bar being arranged to continue the uninterrupted rearward movement of said lost-motion linkage, whereby Ithe latter unlocks said breechblock from said chamber-extension immediately succeeding cessation of movement of said breechblock and said chamber-unit and draws the immobile breechblock rearwardly in said receiver through the remaining portion of its opening stroke.

16. In an automatic rearm, the combination including a receiver; a barrel xed to said receiver; a breechblock reciprocably mounted in said receiver; a chamber-unit comprising a chamber-member slidably supported in said'barrel and a chamber-extension projecting rearwardly into said receiver; a stop-shoulder in said receiver, said shoulder being located rearwardly of the breech-end of said barrel a distance comprising a small fraction of the opening stroke of said breechblock, said shoulder being arranged to project into the path of the rearwardly-moving chamber-extension to stop the rearward movement thereof on discharge of said firearm; breechblock-actuating means comprising an inw ertia-bar and a lost-motion linkage, said linkage being connected to said breechblock, said breechblock-actuating means being arranged to move rearwardly with said breechblock and simultaneouslyfto hold said breechblock in locked engagement with the said chamber-extension of said chamber-unit when said rearm is discharged, whereby said breechblock and said chamber-unit move rearwardly concurrently through the said fractional distance of the opening stroke of said breechblock until said chamber-extension engages said stop-shoulder, the said inertia-bar befing arranged to continue the uninterrupted rearward movement of said lost-motion linkage, whereby the latter unlocks said breechblock from said chamber-extension immediately succeeding cessation of movement of said breechblock and said chamber-unit and draws the immobile breechblock rearwardly lin said receiver through the remaining portion of its opening stroke; and resilient-means carried by said chamber-extension and arranged to abut said stop-shoulder to return said chamber-unit to its normal position in said barrel immediately following disengagement of the breechblock from said chamberextension.

17. In an automatic firearm, the combination including a receiver; a barrel fixed to said receiver; a breechblock reciprocably mounted in said receiver; a chamber-unit comprising chamber-member slidably supported inY s barrel and a chamber-extension projecting c wardly into said receiver, an articulated connection joining said chamber-extension to said chamber-member; a stop-shoulder in said receiver, said shoulder being located rearwardly of the breech-end of said barrel a `distance comprising a small fraction of the opening stroke of said breechblock, said shoulder being arranged to project into the path of the rearwardly-moving chamber-extension to stop the rearward movement thereof on discharge of said firearm; vand breechblock-actuating means comprising an inertia-bar and a lost-motion linkage, said linkage being connected to said breechblock, said breechblock-actuating means being arranged to move rearwardly with said breechblock and simultaneously to hold said breechblock in locked engagement with the said chamber-extension or said chamber-unit when said :firearm is discharged, whereby said breechblock and said chamber-unit move rearwardly concurrently through the said fractional distance of the opening stroke of .said breechblock until said chamber-extension engages said stop-shoulder, 'the said inertia-bar being arranged to continue the uninterrupted rearward movement of said lost-motion linkage, whereby the latter unlocks said breechblock from said chamber-extension immediately succeeding cessation of movement of said breechblock and said chamber-unit and draws the immobile breechblock rearwardly in said receiver through the remaining portion of its opening stroke.

18. In an automatic firearm, the combination including a receiver; a barrel fixed to said receiver; a breechblock reciprocably mounted in said receiver; a chamber-unit comprising a chamber-member slidably supported in said barrel and a chamber-extension projecting rearwardly into said receiver, an articulated connection joining said chamber-extension to said chamber-member; means cooperatively associated with said chamber-unit and said receiver to prevent rotation of said chamber-unit therein; a stop-shoulder in said receiver, said shoulder being located rearwardly of the breech-end o said barrel a distance comprising a small fraction or the opening stroke of said breechblock, said shoulder being arranged to project into the path of the rearwardly-moving chamber-extension to stop the rearward movement thereof on discharge of `said iirearm, and breechblock-actuating means comprising an inertia-bar and a lostmotion linkage, said linkage being connected to said breechblock, said breechblock-actuating means being arranged to move rearwardly with said breechblock and simultaneously to hold said breechblock in locked engagement with the said chamber-extension of said chamber-unit when said rearm is discharged, whereby said breechblock and said chamber-unit move rearwardiy concurrently through the said fractional distance of the opening stroke of said breechblock until said chamber-extension engages said stopshoulder, the said inertia-bar being arranged to continue the uninterrupted rearward movement of said lost-motion linkage, whereby the latter unlocks said breechblock from said chamberextension immediately succeeding cessation of movement of said breechblock and said chamberunit and draws the immobile breechblock rearwardly in said receiver through the remaining portion of its opening stroke.

19. In an automatic firearm, the combination including a receiver; a barrel fixed to said receiver; a breechblock reciprocably mounted in said receiver, said breechblock having an extractor; a chamber-unit comprising a chambermember slidably supported in said barrel and a chamber-extension projecting rearwardly into said receiver, said chamber-extension 'having a keyway constructed and 'arranged to accommodate said extractor so as to prevent rotation of said chamber-unit in said receiver; a stopshoulder in said receiver, said shoulder being located rearwardly of the breech-'end of said barrel a distance comprising a small fraction of the opening stroke of said breechblock, said shoulder being arranged to project into the path of the rearwardly-moving chamber-extension to stop the rearward movement thereof on discharge of said firearm; and breechblock-actuating means comprising an inertia-bar and a lost-motion linkage, said linkage being yconnected. to said breechblock, said breechblock-actuating means being arranged to move rearwardly with said breechblock and simultaneously to hold said breechblock in locked engagement with the said chamber-extension of said chamber-unit when said firearm is discharged, whereby said breechblock and said chamber-unit move rearwardly concurrently through the said fractional distance of the opening stroke of said breechblock until said chamber-extension engages said stopshoulder, the said inertia-bar being arranged to continue the uninterrupted rearward movement of said lost-motion linkage, whereby the latter unlocks said breechblock from said chamber'- eXtension immediately succeeding cessation of movement of said breechblock and said chamberunit and draws the immobile breechblock rearwardly in said receiver through the remaining portion of its opening stroke.

20. In an automatic rearm, -the `combination including a receiver; a barrel fixed to said receiver; a breechblock reciprocably mounted .in said receiver; a lug on said breechblock; a chamber-unit comprising a chamber-member slidably supported in said barrel :and a chamberextension projecting rearwardly into a receiver, said chamber-extension having a bolt-locking shoulder; a stop-shoulder in said receiver, said shoulder being located rearwardly of the breechend of said barrel a distance comprising Aa small fraction of the opening stroke of 'said breechblock, said shoulder being arranged 'to project into the path of the rearwardly-moving :chamberextension to stop the rearward vmovement thereof on discharge of said firearm; and breechblockactuating means `comprising an inertia-bar .and lost-motion linkage connected to said breechblock, said breechblock-actuating means being arranged to move rearwardly with said 'breechblock and simultaneously to hold the breechblock lug in locking engagement with the locking-shoulder of said chamber-extension of said chamber-unit when said rearm is discharged, whereby *said breechblock and said chamber-unit move rearwardly concurrently through the Said fractional distance of the opening `stroke of said lbreechblock until saidv vchamber-eidension engages ysaid stop-shoulder, the said inertia-bar being arranged to continue the uninterrupted rearward ,movement of said lost-motion linkage, whereby 'the latter withdraws the 'lug of said breechblock out of locking engagement with the shoulder oflsaidV the immobile breechblock rearwardly in said receiver through the remaining portion of its opening stroke. Y

DAVID M. WILLIAMS.

No references cited. 

